Thermoplastic resins and blends of thermoplastic resins are used in the production of electronic and optical articles for which light weight, good mechanical strength, heat and dimensional stability are required. As such, thermoplastics such as polycarbonate (PC) and polycarbonate blends such as PC/ABS and PC/PBT have found utility in a wide range of applications.
Some such thermoplastic resins, however, exhibit poor scratch resistance having as low as a B grade of pencil hardness. Poor scratch resistance frequently limits the use of such resins in many applications including in optical, automotive, and electronic industries in which a pencil hardness of at least F and, preferably, at least H is required. Methods have been developed to increase the pencil hardness of polycarbonate including, for example, curing an acrylic coating onto the surface of a polycarbonate-based article. Although successful in increasing the pencil hardness, this method requires an additional step that is expensive and often difficult to control. Another method to improve the pencil hardness uses alloys of polycarbonate and (meth)acrylates, preferably polymethylmethacrylate (pMMA). Although polymethylmethacrylate has a pencil hardness of 2H, pMMA is not compatible with polycarbonate under all processing conditions. Moreover, a relatively high level of poly(meth)acrylate polymer and/or copolymer is required to provide polycarbonate with a hardness increase of at least 3 levels on the pencil hardness scale. Efforts to improve the compatibility through the use of (meth)acrylate copolymers have resulted in increased compatibility and transparency, but insufficient increases in scratch resistance.
A need exists for a modified thermoplastic, and, particularly, a modified polycarbonate-based, composition having an increase of three or more levels of hardness on the pencil hardness scale over the unmodified thermoplastic, and, particularly, polycarbonate-based composition so that such modified thermoplastic and polycarbonate-based resins could be used in a broader range of applications.